This invention relates to novel resinous compositions with high impact resistance, solvent resistance, tensile strength, thermal stability and shear sensitive viscosity, making them uniquely suitable for extrusion and blow molding. More particularly, it relates to improved compositions comprising polyphenylene ethers and linear polyesters.
The polyphenylene ethers are a widely used class of thermoplastic engineering resins characterized by excellent hydrolytic stability, dimensional stability, toughness, heat resistance and dielectric properties. They are also resistant to high temperature conditions under many circumstances. Because of the brittleness of many compositions containing polyphenylene ethers, they are frequently blended with impact modifiers such as elastomers to form molding compositions.
A disadvantage of the polyphenylene ethers which militates against their use for molding such items as automotive parts is their low resistance to non-polar solvents such as gasoline. For increased solvent resistance, it would be desirable to blend the polyphenylene ethers with resins which have a high degree of crystallinity and therefore are highly resistant to solvents. Illustrative of such resins are the linear polyesters including poly(alkylene dicarboxylates), especially the poly(alkylene terephthalates). However, such blends frequently undergo phase separation and delamination. They typically contain large, incompletely dispersed polyphenylene ether particles and no phase interaction between the two resin phases. Molded parts made from such blends are typically characterized by extremely low impact strength.
In copending, commonly assigned U.S. patent application Ser. No. 891,457, filed July 29, 1986, there are disclosed highly compatible, impact and -solvent-resistant polymer blends containing polyphenylene ethers and poly(alkylene dicarboxylates), and resinous molding compositions suitable for use in the fabrication of automotive parts and the like. That invention is based on the discovery of a new genus of compatible blends containing polyphenylene ethers and poly(alkylene dicarboxylates) in weight ratios as high as 1:1, or even higher under certain circumstances, and a method for their preparation. According to that application, there are also incorporated in the resinous composition an impact modifier compatible with the polyphenylene ether component and a compatibilizing agent containing a substantial proportion of aromatic polycarbonate structural units. Among the impact modifiers disclosed to be useful in such compositions were various elastomeric copolymers of which examples were ethylene-propylene-diene polymers (EPDM's); carboxylated ethylene propylene rubbers; block copolymers of styrene with dienes and core-shell elastomers containing, for example, a rubbery polyacrylate phase and a polystyrene phase.
In copending commonly assigned U.S. patent application Ser. No. 37,763, filed Apr. 13, 1987, there are disclosed impact resistant polyphenylene ether and linear polyester compositions in which the impact modifier comprises a glycidyl methacrylate or acrylate grafted onto a rubber olefin polymer backbone, especially preferably, an EPDM backbone. In the mentioned application, it is stated to be important that the polyphenylene ether resin be functionalized, e.g., by reaction with an anhydride, before being impact modified, thus perhaps providing a chemical reaction between the resin and the modifier. In the disclosed compositions, however, there are certain drawbacks, even though they are eminently suitable for many uses. Polyphenylene ether resin compositions alone tend to lack chemical resistance making them relatively unsuitable for use, for example, around solvents and motor fuels. The polyester compositions, or the other hand, provide enhanced chemical resistance and heat resistance, but the blends with polyphenylene ethers are somewhat brittle when molded and when an impact modifier is added, such as a styrene-ethylene-butylene-styrene block copolymer, they provide molded articles which are very brittle.
If, however, a compatibilizing agent containing a substantial proportion of aromatic polycarbonate structural units is used in combination with a glycidyl methacrylate or glycidyl acrylate grafted EPDM rubber as an impact modifier for polyphenylene ether-polyester compositions an unexpected improvement in ductility is achieved and as a result there is seen a substantial improvement in the impact strength of articles molded from such compositions, and this is true whether or not a functionalized polyphenylene ether is used. While the reasons for the foregoing are not clearly understood at this time, it is believed that the particular modifier used is chemically reactive with the polyester component whereas the prior composition used impact modifiers tending to be compatible with the polyphenylene ether component exclusively. Thus the present compositions, in contrast to the prior compositions, are believed to be impact modified through the polyester phase, and are thus morphologically distinct.